Row-level security must be enabled on the table by using ALTER TABLE... ENABLE ROW LEVEL SECURITY in order for creating policies to be applied. If row-level security is enabled for a table, but no applicable policies exist, a default deny policy is assumed that no rows will be visible or updatable.
Can RLS or CLS be treated as a SELECT trigger, or is it too coarse for that?
I agree with the suggestion to use a view if possible. I know it might not be viable if you use an object-relational model abstraction layer implementation that provides heavy caching.